The objective of this research program is to better understand the pitch perception of narrowband complex sounds by human observers. The specific aim of the research includes 1) to examine the validity of the predictions of two competing models (EWAIF and sewaif) on narrowband pitch, and 2) to conduct a systematic investigation on the pitch of narrowband sounds. The EWAIF model derives pitch from an envelope-weighted time average of instantaneous frequency of the waveform, whereas the SEWAIF model derives the pitch from a square-of-the-envelope weighted average of instantaneous frequency. The experimental paradigm requires the observer to match the pitch of a test stimulus with the pitch of a standard stimulus. The test stimuli are chosen such that the EWAIF and SEWAIF models predict different pitch values, an the standard stimuli are chosen such that the two models predict athe same pitch value. Pitch matching experiments using those stimuli can determine which model is a better predictor of the data. In addition to testing between the two models, the proposed study will examine the effects of stimulus level, center frequency, phases, spectral bandwidth, envelope fluctuation, and masking stimulus using various stimuli. A systematic study of the pitch of narrowband sounds will help hearing scientists to understand pitch perception in more quantitative detail. The basic information obtained from such studies will expand the current knowledge about the auditory system and may thus be useful for diagnosis and treatment of auditory impairment.